1. Field of the Invention
The present invention relates to an epitaxial structure of semiconductor device and a manufacturing method thereof, more particularly, to an epitaxial structure of semiconductor device with improved strain effect and a manufacturing method thereof.
2. Description of the Prior Art
The semiconductor integrated circuit (IC) industry has experienced rapid growth. In the course of IC evolution, strained source/drain features have been implemented using epitaxial (EPI) semiconductor materials to enhance carrier mobility and improve device performance. For example, when forming a metal-oxide-semiconductor field effect transistor (MOSFET), silicon germanium (SiGe) may be epitaxially grown to form source and drain features. Various techniques directed at shapes, configurations, and materials of these source and drain features have been implemented to further improve transistor device performance. Although many approaches have been developed for their intended purposes, they have not been entirely satisfactory in all respects. For example, in a conventionally formed SiGe bulk structure, the Ge concentration in Ge region is not as high as expectation, and the Ge region with higher concentration has a certain distance to channel region.